An air conditioner has a refrigerant circuit in which an outdoor-side heat exchanger, an expansion valve, and an indoor-side heat exchanger are connected with a compressor in a loop form by refrigerant pipes via a four-way switching valve. In the air conditioner, by switching the flow direction of a refrigerant by means of the four-way switching valve, either of cooling operation and heating operation is set.
A compressor used for this refrigerant circuit is broadly classified into an internal high pressure type and an internal low pressure type. FIG. 20 shows a refrigerant circuit using an internal high pressure type compressor 1A, and FIG. 21 shows a refrigerant circuit using an internal low pressure type compressor 1B.
The basic configurations of the compressors 1A and 1B are the same. The compressor of either type has a cylindrical enclosed vessel 2, and the enclosed vessel 2 contains a refrigerant compressing section 3 and an electric motor 4. Although not shown in detail, the refrigerant compressing section 3, being of a scroll type, has a compression chamber formed by engaging a fixed scroll having a spiral wrap on an end plate with an orbiting scroll driven by the electric motor 4.
The interior of the enclosed vessel 2 is divided into two chambers by the end plate on the side of the fixed scroll in the refrigerant compressing section 3. One of these two chambers is a refrigerant discharge chamber 5 provided on the side of a discharge port 3a of the refrigerant compressing section 3. The other is an electric motor chamber 6 in which the electric motor 4 is contained. Also, the electric motor chamber 6 is provided with a bearer plate 7 which pivotally supports a driving shaft 4a of the electric motor 4. A subsidiary electric motor chamber 6a is formed on the side opposite to the refrigerant discharge chamber 5 of the electric motor chamber 6 by the bearer plate 7. The bearer plate 7 is formed with an arbitrary number of refrigerant flowing holes 7a.
Either of the compressors 1A and 1B is connected, via a four-way switching valve 8, with a heat exchanging circuit in which an outdoor-side heat exchanger 9, an expansion valve (or a capillary tube) 10, and an indoor-side heat exchanger 11 are connected in a loop form by refrigerant pipes.
The configurations of the internal high pressure type compressor 1A and the internal low pressure type compressor 1B differ in the following respects: That is, in the internal high pressure type compressor 1A shown in FIG. 20, the refrigerant discharge chamber 5 communicates with the electric motor chamber 6 via a communicating path 12, and a suction pipe 13 for low-pressure refrigerant drawn from the four-way switching valve 8 is directly connected to a suction port 3b of the refrigerant compressing section 3.
Contrarily, in the internal low pressure type compressor 1B shown in FIG. 21, the refrigerant discharge chamber 5 and the electric motor chamber 6 are independent of each other. The suction port 3b of the refrigerant compressing section 3 is opened on the side of the electric motor chamber 6, and the suction pipe 13 drawn from the four-way switching valve 8 is connected to the electric motor chamber 6.
The following is a description of the operations of the compressors 1A and 1B. FIG. 20 shows a state at the time of cooling operation using the internal high pressure type compressor 1A. A low-pressure refrigerant from the indoor-side heat exchanger 11 is sucked into the refrigerant compressing section 3 through the suction pipe 13. After being compressed, the refrigerant is discharged into the refrigerant discharge chamber 5 as a high-temperature high-pressure refrigerant gas. This high-temperature high-pressure refrigerant gas is supplied to the outdoor-side heat exchanger 9 through a discharge pipe 14 for high-pressure refrigerant and the four-way switching valve 8. Also, some of the high-temperature high-pressure refrigerant gas flows into the electric motor chamber 6 through the communication path 12. Thereby, the compressor 1A is classified as the internal high pressure type.
For the internal high pressure type, the discharge pipe 14 for high-pressure refrigerant is connected to the side of the subsidiary electric motor chamber 6a, not to the refrigerant discharge chamber 5, as indicated by the chain line in FIG. 20 so that a high-pressure refrigerant is introduced from the subsidiary electric motor chamber 6a to the four-way switching valve 8.
At the time of heating operation, the four-way switching valve 8 is turned 90 degrees from the state shown in FIG. 20, so that the discharge pipe 14 for high-pressure refrigerant is connected to the indoor-side heat exchanger 11, and the suction pipe 13 for low-pressure refrigerant is connected to the outdoor-side heat exchanger 9.
FIG. 21 shows a state at the time of heating operation using the internal low pressure type compressor 1B. The low-pressure refrigerant from the outdoor-side heat exchanger 9 flows into the electric motor chamber 6 through the suction pipe 13, so that the interior thereof becomes low in pressure. The low-pressure refrigerant is sucked into the refrigerant compressing section 3 through the suction port 3b. After being compressed, the refrigerant is discharged into the refrigerant discharge chamber 5 as a high-temperature high-pressure refrigerant gas, and is supplied to the indoor-side heat exchanger 11 through the discharge pipe 14 and the four-way switching valve 8. At the time of cooling operation; the four-way switching valve 8 is turned 90 degrees from the state shown in FIG. 21, so that the discharge pipe 14 for high-pressure refrigerant is connected to the outdoor-side heat exchanger 9, and the suction pipe 13 for low-pressure refrigerant is connected to the indoor-side heat exchanger 11.
In either of the internal high pressure type and the internal low pressure type, an object of introducing the refrigerant into the electric motor chamber is to prevent overheat of the electric motor, and these two types have advantages and disadvantages as described below.
In case of the internal high pressure type, since a lubricating oil can be separated from the refrigerant gas in the electric motor chamber, the lubricating oil is positively supplied into the compressor, by which good sealing can be provided between rubbing portions of the fixed scroll and the orbiting scroll in the refrigerant compressing section. Also, by making the interior of the electric motor chamber high in pressure, a thrust force applied to the orbiting scroll can be controlled easily, and the load on the electric motor can be decreased. Accordingly, the power consumption can be lowered.
Also, in case of the internal high pressure type, since the temperature of the enclosed vessel is higher than the ambient temperature at the time of cooling operation, the heat dissipation amount is increased, so that the cooling capacity can be increased. However, the internal high pressure type is disadvantageous in terms of heating capacity because the amount of heat dissipating from the enclosed vessel is large.
On the other hand, in case of the internal low pressure type, since the temperature of the enclosed vessel is approximately equal to the ambient temperature at the time of heating operation, the amount of heat dissipating from the enclosed vessel is small, so that the heating capacity is high. In particular, comparing with the internal high pressure type in which the high-pressure refrigerant is discharged from the subsidiary electric motor chamber through the electric motor chamber, the internal low pressure type has a high rising property at the start time of heating operation.
Specifically, the refrigerant, which has been accumulated in the compressing section at the time of stoppage, is compressed simultaneously with the start, and the high-temperature high-pressure refrigerant gas is directly supplied to the indoor-side heat exchanger, not being caused to pass through the electric motor chamber, unlike the internal high pressure type. Therefore, a sufficient refrigerant circulating amount is secured from the start, so that the temperature is increased properly.
However, in the case of the internal low pressure type, the lubricating oil supplied to the compressor is not separated from the refrigerant gas, and is discharged to the heat exchanging circuit. Therefore, not only the heat exchange capacity is decreased, but also the rubbing portions of the scroll may be seized by the shortage in the lubricating oil in the compressor.
Also, the internal low pressure type is liable to cause decreased performance because the sucked refrigerant gas is caused to pass through the electric motor chamber and is overheated by the heat in the electric motor chamber, whereby the density of the refrigerant gas is made low.